136 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



planted plat had an average height of 6.9 feet and a diameter of 33.4 mm. 

 One of the tallest plants was 8.3 feet high. They were in seed, some having 

 flower-heads 8 inches in diameter. 



The number and size of the plants in the thickly planted area in each site is 

 summarized in table 15 : 



Table 15. — Development of sunflowers. 



The root development in the middle of the thickly planted areas was 

 thoroughly studied. In the lower plat it was found that the roots were not at 

 all abundant below the surface foot of soil and they were very scarce below 2 

 feet. The soil in this plat was exceedingly dry and hard when compared with 

 adjacent areas. Even the largest sunflowers in the area had very much more 

 poorly developed root systems than those of the thin planting shown in figure 

 37. Not only were there far fewer laterals, but they were much less extensive 

 and more poorly branched. A few tap-roots of the larger plants were traced 

 to a maximum depth of 3.8 feet. In the upper plats the roots were even more 

 poorly developed. Few occurred below 10 inches. The laterals were not so 

 widely spread as in the plants in the lower plats. Several of the larger tap- 

 roots ended at a depth of about 3 feet, but one with an unusually large 

 diameter was traced to the 4.6-foot level. It gave off no large branches below 

 10 inches, although short ones occurred nearly to the tip. The last foot of the 

 root, which was 1.5 mm. thick, had no branches, but was densely covered with 

 root-hairs. It appears from this experiment that just as competition between 

 individual sunflowers growing close together inhibits the normal development 

 of the above-ground parts, it affects the roots in a similar manner (Weaver, 

 1918 : 279) . The plants in the upper plats which had the poorer stem develop- 

 ment also had a poorer root-growth. Of the lowland plants, those in the 

 crowded area had a much poorer stem and root development than those in the 

 thinly planted plat. Under the latter condition in both areas the numerous 

 lateral roots obliqued downward to a much greater extent and reached 

 greater depths than those in the thick planting. Even the dominant individ- 

 uals in the crowded areas matured earlier and dried up more rapidly than 

 their larger, deeper-rooted neighbors in adjoining plats. 



White clover (Trifolium repens).— On July 11 the plants of white clover 

 were 3 and 5 inches high in the upper and lower plats respectively. In the 

 latter habitat the tap-roots were 2 to 2.5 mm. in diameter and penetrated to a 

 working level of 2.5 feet. This was the same depth determined for plants 

 growing in the upland soil. In general, the root-habit was not greatly unlike 

 that of red clover. The stand on both sites was poor and further studies were 

 not made. 



